Joints between bells (tubular members) and spigots for connecting plastic pipe sections together employing a resilient, yieldable gasket therebetween are not new. Such joints comprise a gasket normally secured in a recess of a bell or tubular end at the expanded end of the tubular member (a pipe fitting or coupling for example) for sealing against the outer end surface of a spigot. Such joints offer a quick method of pipe installation which is economical and easy to assemble, thereby eliminating the need for skilled pipe fitting personnel and permitting semi-skilled installers to form the joint. However, as the reader will appreciate, the formation of the seal is paramount. If a satisfactory seal is not the end result of inserting the spigot end into the bell or tubular end of the tubular member (pipe fitting or coupling), then the resultant losses and the ultimate repair can be extremely costly, for example, where the pipe has been buried or embedded in concrete. Hence, the seal created must continue to exist under all conditions to preclude a leakage radially inwardly into the pipe or radially outwardly from the pipe, or both, depending on the application (for example, vacuum, low pressure, high pressure situations) and to ensure the seal is maintained even where there is a shifting in the spigot-bell connection of the pipe buried in the ground. As a result of these requirements, many industry standards have been established, for example, ASTM, and CSA testing criteria to verify the integrity of seals at joints of various applications. In one application, a sewer pipe joint must be able to withstand a test of applied pressure at 10.8 p.s.i. gauge for 10 minutes without a reduction in that pressure. In vacuum applications the tests have required that the pipe system joint must hold 22 inches of mercury for 20 minutes without the gasket joint leaking more than 1 inch of mercury in the first 10 minutes and without the joint leaking more than 5 inches of mercury in the second 10 minute period (see ASTM D3212 Standard).
In order to ensure the integrity of the seal, the gasket must be of such shape and size as to permit uniform annular compression applied by the spigot of the pipe as the spigot is inserted into the bell and after assembly, maintain the positive seal under all conditions applied to the joint. Further, the gasket must prove reliable over a long period of time in use and not sag, elongate, move, slip or disintegrate and must remain pliable, resilient and firm in its intended position to maintain the seal first created. (Applicant directs the reader's attention to ASTM-476 and F477 and CSA standards B182.1 and B182.2 [M1983].)
As a result of the stringent requirements, many different methods and configurations have been proposed for creating a seal using a gasket in a bell between the bell and the spigot. For example, U.K. Patent No. 1,168,040 teaches a pipe coupling employing a bell (tubular member) with a radially inturned lip to retain a sealing ring and an incompressible locking ring dividing the ring into three parts. Other joints are taught in German Patent No. 2,205,532, U.S. Pat. No. 3,915,460, U.S. Pat. No. 3,217,092, U.S. Pat. No. 4,034,994, German Patent No. 1,118,551, U.S. Pat. No. 4,097,074, U.K. Patent No. 1,033,756 and U.S. Pat. No. 4,143,884. Compound elastomeric elements for assisting to create a seal for example, having more than one resilient member working in unison, are taught in U.S. Pat. No. 2,272,811 and U.S. Pat. No. 3,265,410.
U.S. Pat. Nos. 2,146,641, 2,980,449, 3,265,410, 3,503,619, and 4,018,461 teach further gasket-bell configurations used in an attempt to form more secure joints. U.S. Pat. Nos. 2,953,398, 2,991,092, 3,244,797, 3,315,971, 4,097,074, and 4,343,480 (corresponding to Canadian Letters Patent No. 1,158,277), teach various gasket formations having forward and rearward restraining surfaces including a rearward corner for supporting a gasket in a further attempt to provide an improved joint. U.S. Pat. No. 3,520,047 teaches the shaping of the end of the pipe bell from thermoplastic material as well as a form of elastomeric joint in an attempt to provide an improved joint. The method taught by the said Patent teaches a deforming core (see FIG. 9) around which a thermoplastic pipe bell may be formed.
U.S. Pat. No. 3,362,717 is another attempt to provide a suitable joint, teaching the use of a rearward shoulder section of the gasket acting with the bell in unison to provide reinforcement of the seal's ability to remain fixed in its sealing position. The addition of the sheath shown in FIG. 1 is taught to enhance the sealing properties of the joint by coming in contact with 15A of FIG. 2 and area 5 of FIG. 1 of the main gasket.
U.S. Pat. No. 3,741,570 teaches a flexible joint for a sewer pipe with a blunt-cut spigot end. The formed joint comprises a forward shoulder or surface and rearward shoulder or edge upon which the gasket abuts during compression and insertion of the spigot end whereby the rearward shoulder prevents, according to the teachings of the Patent, the gasket from rolling out of position during the insertion process.
U.S. Pat. No. 2,620,206 discloses a pipe coupler seal which incorporates latches and keepers 15 and 14 respectively as shown in FIG. 1, which purport to secure split collar 17 in place. Wall 23 seen in FIG. 3 has been formed by cutting radially outwardly from the inner surface of the coupling to provide an abutment shoulder 21a and annular walls 22 and 23 for receiving gasket 12. Gasket 12 is inserted into the completed groove and thus if inserted can be removed.
In the same vein as U.S. Pat. No. 2,620,206, Applicant has become aware subsequent to its invention to a pipe and a bell joint manufactured by Dyka International BV of Amsterdam, Holland which incorporates the front of a gasket being secured by a bent-forward lip and which gasket, extends rearwardly along the inner surface of the bell.
It is therefore an object of this invention to provide an improved joint between the bell of a pipe fitting or coupling (end of a tubular member) and spigot, incorporating a gasket secureably mounted in the bell in a simple yet highly reliable manner to provide a more effective and reliable seal which seal, when formed by semi-skilled or even unskilled workers, is easily formed. It is a further object of the invention to provide improved components therefor, including gasket and bell. It is still a further object of the invention to provide an improved gasket-bell assembly for use to form the improved joint and method for securing the gasket in the bell.
It is a further object of this invention to firmly secure the elastomeric gasket seat at its forward and rearward ends without the need of cements or adhesives. It is a further object of this invention to provide a configuration of a bell on the end of a pipe fitting or coupling (end of a tubular member) which, when used to secure a gasket during assembly, so secures the gasket in the bell (end of tubular member) such that it remains so during use. It is a further object of the invention to provide a method of manufacturing the bell carrying the gasket (end of the tubular member carrying the gasket).
Further and other objects of the invention will be apparent to those skilled in the art from the following summary of the invention and detailed description of embodiments thereof.